1. Field of The Invention
The present invention relates to the field of voltage regulators. More particularly the present invention relates to the field of voltage regulators with servo loops.
2. Description of The Prior Art
The following eleven (11) prior art references are related to regulated power supplies or voltage or current regulators:
1. U.S. Pat. No. 3,315,149 issued to Strait et al. on Apr. 18, 1967 for "High Stability Regulated Voltage Supply" (hereafter the "Strait Patent").
2. U.S. Pat. No. 3,986,101 issued to Koetsch et al on Oct. 12, 1976 for "Automatic V-I Crossover Regulator" (hereafter the "Koetsch Patent").
3. U.S. Pat. No. 4,254,372 issued to Moore, Jr. on Mar. 3, 1981 for "Series Pass Voltage Regulator with Overcurrent Protection" (hereafter the "Moore Patent").
4. U.S. Pat. No. 4,321,525 issued to Imazeki et al. on Mar. 23, 1982 for "Reference Voltage Generating Circuit In A DC Power Supply" (hereafter the "Imazeki Patent").
5. U.S. Pat. No. issued 4,326,245 to Saleh on Apr. 20, 1982 for "Current Foldback Circuit For A DC Power Supply" (hereafter the "Saleh Patent").
6. U.S. Pat. No. 4,327,319 issued to Swisher et al. on Apr. 27, 1982 for "Active Power Supply Ripple Filter" (hereafter the "Swisher Patent").
7. U.S. Pat. No. 4,481,462 issued to de Kleijn on Nov. 6, 1984 for "Amplitude Control System" (hereafter the "de Kleijn Patent").
8. U.S. Pat. No. 4,502,152 issued to Sinclair on Feb. 26, 1985 for "Low Current Linear/High Current Chopper Voltage Regulator" (hereafter the "Sinclair Patent").
9. U.S. Pat. No. 4,543,522 issued to Moreau on Sep. 24, 1985 for "Regulator with A Low Drop-out Voltage" (hereafter the "Moreau Patent").
10. U.S. Pat. No. 4,728,901 issued to Pepper on Mar. 1, 13, 1988 for "Power Buffer Circuit" (hereafter "Peper Patent").
11. U.S. Pat. No. 4,771,226 issued to Jones on Sep. 13, 1988 for "Voltage Regulator For Low Voltage, Discharging Direct Current Power Source" (hereafter the "Jones Patent").
12. U.S. Pat. No. 4,866,585 issued to Das on Sep. 12, 1984 for "AC to DC Solid State Power Supply Using High Frequency Pulsed Power Switching" (hereafter the "Das Patent").
13. U.S. Pat. No. 4,983,905 issued to Sano et al. on Jan. 8, 1991 for "Constant Voltage Source Circuit" (hereafter the "Sano Patent").
14. IBM Technical Disclosure Bulletin, Vol. 21, No. 2, authored by J. S. Tung and published in July 1978 for "Controlled Saturation Compensation For Power Amplifier" (hereafter the "IBM article").
15. The Encyclopedia of Electronic Circuits, 1st ed., authored by Rudolf F. Graf and published in 1985, pages 280, 288 and 501 (hereafter "the Graf book").
The Strait Patent discloses a high stability voltage regulated power supply. The Strait Patent circuit is connected between the input voltage E.sub.i and the output voltage E.sub.o includes a voltage regulator, a differential amplifier and a direct current (DC) amplifier. The output voltage E.sub.o is sampled by a ratio network of resistors which are connected in series across E.sub.o. The sample voltage is then compared to that of a standard voltage reference, and the difference between the two voltages is treated as an error signal and fed to the DC amplifier. The error signal is amplified, inverted and fed to one input terminal of the differential amplifier. The output of the regulator is coupled to the other terminal of the differential amplifier; and therefore the high-speed transients induced by the rapidly switching loads are corrected. The Koetsch Patent discloses an automatic V-I crossover regulator. It teaches the operation of two or more identical power supplies operating in parallel to provide voltage regulated direct current to a single load. The voltage regulator circuit in the Koetsch Patent has no servo loop, but works as an operational amplifier using negative feedback. The input D.C. voltage is not actually a reference voltage (since no servo is used), but rather an input voltage for direct amplification. The two power sources and all the reference voltage must be isolated from one another, or the current sensing used will not be able to detect the output current of its own respective regulator.
The Moore Patent discloses a series pass voltage regulator with overcurrent protection. The Moore Patent circuit includes a series pass transistor used as a regulator, an amplifier for adjusting the base current of the transistor, a transistor used for shunting the drive current to the amplifier, and a differential amplifier for controlling the shunting function of the transistor according to the sensed output voltage. A reference voltage is provided to the differential amplifier. When the output voltage is higher than the desired value, the differential amplifier will increase its output. The bias current for transistors is therefore increased to increase the amount of current shunted through the transistor. The amplifier then conducts less base drive current to a transistor whose conduction is thereby reduced to decrease the output voltage of the regulator.
The Imazeki Patent discloses a reference voltage generating circuit in a DC power supply. It is a single servo loop voltage regulator with improvement on the reference voltage circuit.
The Saleh Patent discloses a current foldback circuit for a DC power supply. The Saleh Patent circuit includes a comparator which compares the output current with a reference and produces a current foldback signal if the output current exceeds the desired level. The current foldback signal is sent to a differential amplifier which produces a control signal to the output stage of the circuit for reducing and modifying the amount of output accordingly.
The Swisher Patent discloses an active power supply ripple filter. It is also a single servo loop voltage regulator.
The de Kleijn Patent discloses an amplitude control system. It is not a voltage regulated power supply or voltage regulator.
The Sinclair Patent discloses a low current linear/high current chopper voltage regulator. It is also a single servo loop voltage regulator with improvement on the reference voltage circuit.
The Moreau Patent discloses a regulator with a low drop-out voltage. It is again a single servo loop voltage regulator specially designed for use with a low drop-out voltage.
The Pepper Patent discloses a power buffer circuit which includes a differential amplifier and an error amplifier connected in local feedback relation directly to the differential amplifier. It teaches a specific connection between a MOSFET transistor and a bipolar transistor to create a unity gain. The differential amplifier amplifies the power of an input signal to produce an output signal. The error amplifier adjusts the differential amplifier to cause the voltage level of the output signal to follow the voltage level of the input signal. The error amplifier samples the output signal voltage and the input signal voltage to sense a difference between the signal voltages. In response to a difference, the error amplifier signals the differential amplifier to change the voltage level of the output signal. The Pepper Patent utilizes a power buffer circuit which is connected to an external voltage sense circuit to form a voltage regulator. The power buffer uses a linear negative feedback arrangement to establish a "unity" voltage gain between its input and output.
The Jones Patent discloses a voltage regulator for a low voltage, discharging direct current power source. It is again a single servo loop voltage regulator primarily designed for a single cell low voltage power supply.
The Das Patent discloses an AC to DC solid state power supply using high frequency pulsed power switching. It includes (a) auxiliary power supply, (b) input rectifier/filter, (c) input switching circuit, (d) isolating transformer, (e) control circuit, (f) magnetic circuit, (g) output rectifier/filter, (h) heat distribution element, and (i) packaging. The Das Patent utilizes transformers within the circuit. The Das Patent teaches an optoisolator for sensing the output voltage. In the Das Patent, outsense loop uses the optoisolator not as a comparator or threshold detector but simply as a linear isolator/voltage buffer.
The Sano Patent discloses a constant voltage source circuit. It is also not a voltage regulated power supply or voltage regulator.
The IBM article discloses a controlled saturation compensation for a power amplifier. It is again not a voltage regulated power supply or voltage regulator.
The Graf book discloses certain electronic circuits which utilize filters.
Today, many regulated power supplies have utilized inner servo loops to control the output of the voltage regulated power supply. However, to compensate the voltage drop occurring between the output of the power supply and the actual load, which is often caused by the conductive resistance of the long conducting wires, an outer servo loop is often needed. Nevertheless, there is no teaching in the prior art to provide an interfacing block in between the inner servo loop and the outer servo loop which can make the two servo loops act in a cohesive manner.
It is desirable to provide a new functional control block to be connected between the inner servo loop of a voltage regulator and the outer servo loop of the circuit, which can make the outer servo loop adaptable to the inner servo loop.